Effects of Rhizoctonia infection and drought on peroxidase and chitinase activity in Norway spruce (Picea abies)

Piriformospora indica Primes Onion Response against Stemphylium Leaf Blight Disease

The root-endophytic fungus Piriformospora indica (=Serendipita indica) has been revealed for its growth-promoting effects and its capacity to induce resistance in a broad spectrum of host plants. However, the bioefficacy of this fungus had not yet been tested against any pathogen affecting onion (Allium cepa). In this study, the biocontrol potency of P. indica against onion leaf blight, an impacting disease caused by the necrotrophic fungal pathogen Stemphylium vesicarium, was evaluated. First, it was proved that colonisation of onion roots by P. indica was beneficial for plant growth, as it increased leaf development and root biomass. Most relevantly, P. indica was also effective in reducing Stemphylium leaf blight (SLB) severity, as assessed under greenhouse conditions and confirmed in field trials in two consecutive years. These investigations could also provide some insight into the biochemical and molecular changes that treatment with P. indica induces in the main pathways associated with host defence response. It was possible to highlight the protective effect of P. indica colonisation against peroxidative damage, and its role in signalling oxidative stress, by assessing changes in malondialdehyde and H2O2 content. It was also showed that treatment with P. indica contributes to modulate the enzymatic activity of superoxide dismutase, catalase, phenylalanine ammonia-lyase and peroxidase, in the course of infection. qPCR-based expression analysis of defence-related genes AcLOX1, AcLOX2, AcPAL1, AcGST, AcCHI, AcWRKY1, and AcWRKY70 provided further indications on P. indica ability to induce onion systemic response. Based on the evidence gathered, this study aims to propose P. indica application as a sustainable tool for improving SLB control, which might not only enhance onion growth performance but also activate defence signalling mechanisms more effectively, involving different pathways.

Transcript Dynamics in Wounded and Inoculated Scots Pine

Comparative transcriptome analysis provides a useful tool for the exploration of plant-pathogen interaction by allowing in-depth comparison of gene expression between unaffected, inoculated and wounded organisms. Here we present the results of comparative transcriptome analysis in genetically identical one-year-old Scots pine ramets after wounding and inoculation with Heterobasidion annosum. We identified 230 genes that were more than 2-fold upregulated in inoculated samples (compared to controls) and 116 downregulated genes. Comparison of inoculated samp les with wounded samples identified 32 differentially expressed genes (30 were upregulated after inoculation). Several of the genes upregulated after inoculation are involved in protection from oxidative stress, while genes involved in photosynthesis, water transport and drought stress tolerance were downregulated. An NRT3 family protein was the most upregulated transcript in response to both inoculation and wounding, while a U-box domain-containing protein gene was the most upregulated gene comparing inoculation to wounding. The observed transcriptome dynamics suggest involvement of auxin, ethylene, jasmonate, gibberellin and reactive oxygen species pathways and cell wall modification regulation in response to H. annosum infection. The results are compared to methyl jasmonate induced transcriptome dynamics.

Comparative transcriptional and metabolic responses of Pinus pinea to a native and a non-native Heterobasidion species

Heterobasidion irregulare is a causal agent of root and butt-rot disease in conifers, and is native to North America. In 1944 it was introduced in central Italy in a Pinus pinea stand, where it shares the same niche with the native species Heterobasidion annosum. The introduction of a non-native pathogen may have significant negative effects on a naïve host tree and the ecosystem in which it resides, requiring a better understanding of the system. We compared the spatio-temporal phenotypic, transcriptional and metabolic host responses to inoculation with the two Heterobasidion species in a large experiment with P. pinea seedlings. Differences in length of lesions at the inoculation site (IS), expression of host genes involved in lignin pathway and in cell rescue and defence, and analysis of terpenes at both IS and 12 cm above the IS (distal site, DS), were assessed at 3, 14 and 35 days post inoculation (dpi). Results clearly showed that both species elicit similar physiological and biochemical responses in P. pinea seedlings. The analysis of host transcripts and total terpenes showed differences between inoculation sites and between pathogen and mock inoculated plants. Both pathogen and mock inoculations induced antimicrobial peptide and phenylalanine ammonia-lyase overexpression at IS beginning at 3 dpi; while at DS all the analysed genes, except for peroxidase, were overexpressed at 14 dpi. A significantly higher accumulation of terpenoids was observed at 14 dpi at IS, and at 35 dpi at DS. The terpene blend at IS showed significant variation among treatments and sampling times, while no significant differences were ever observed in DS tissues. Based on our results, H. irregulare does not seem to have competitive advantages over the native species H. annosum in terms of pathogenicity towards P. pinea trees; this may explain why the non-native species has not widely spread over the 73 years since its putative year of introduction into central Italy.

Cloning and characterization of chitinases from interior spruce and lodgepole pine

Chitinases have been implicated in the defence of conifers against insects and pathogens. cDNA for six chitinases were cloned from interior spruce (Picea glauca x engelmannii) and four from lodgepole pine (Pinus contorta). The cloned interior spruce chitinases were annotated class I PgeChia1-1 and PgeChia1-2, class II PgeChia2-1, class IV PgeChia4-1, and class VII PgeChia7-1 and PgeChia7-2; lodgepole pine chitinases were annotated class I PcChia1-1, class IV PcChia4-1, and class VII PcChia7-1 and PcChia7-2. Chitinases were expressed in Escherichia coli with maltose-binding-protein tags and soluble proteins purified. Functional characterization demonstrated chitinolytic activity for the three class I chitinases PgeChia1-1, PgeChia1-2 and PcChia1-1. Transcript analysis established strong induction of most of the tested chitinases, including all three class I chitinases, in interior spruce and lodgepole pine in response to inoculation with bark beetle associated fungi (Leptographium abietinum and Grosmannia clavigera) and in interior spruce in response to weevil (Pissodes strobi) feeding. Evidence of chitinolytic activity and inducibility by fungal and insect attack support the involvement of these chitinases in conifer defense.

Gene expression profiling of a compatible interaction between Douglas-Fir and the root rot fungal pathogen Phellinus sulphurascens

Douglas-fir (DF) (Pseudotsuga menziesii) is one of the largest and most economically important coniferous species in western North America. Its productivity is greatly affected by the root rot fungus Phellinus sulphurascens Pilát. Evidence of resistance by DF to fungal root pathogens such as P. sulphurascens has been reported but mechanisms of resistance in this compatible pathosystem are not yet known. To better understand the DF-P. sulphurascens interaction, especially at the molecular level, we selected 12 diverse plant genes already identified as defense-related from a cDNA library constructed using root tissues from P. sulphurascens-infected DF seedlings. Using quantitative reverse-transcriptase polymerase chain reaction on infected DF root samples collected at five different time points after inoculation, we found that P. sulphurascens infection significantly elevated expression of the 12 selected genes. In most cases the highest expression level was recorded within 2 to 3 days after inoculation. The constructed cDNA library, which is enriched with defense-related host genes and a number of fungal genes, will continue to serve as a useful resource for future larger-scale gene discovery and functional research on the P. sulphurascens and DF pathosystem.

Biotransformation of the fungal phytotoxin fomannoxin by soil streptomycetes

Rhizosphere-associated Streptomyces sp. AcH 505 (AcH 505) promotes infection of Norway spruce (Picea abies) with the pathogenic fungus Heterobasidion abietinum 331, while Streptomyces sp. GB 4-2 (GB 4-2) enhances spruce defense against the fungus. To identify whether these bacteria influence the availability of the fungal phytotoxin fomannoxin and hence spruce infection, we analyzed the fomannoxin yield in H. abietinum 331-AcH 505 dual cultures. Further, the fate of fomannoxin was studied by adding the compound to cultures of AcH 505, GB 4-2 and nine other soil streptomycetes. Culture filtrates were extracted with ethyl acetate and analyzed by HPLC. Structures of novel compounds were elucidated by HPLC-HR-ESI-Orbitrap-MS and NMR spectroscopy. Phytotoxicity of the compounds was determined by in vivo measurement of maximum photosystem II efficiency of Arabidopsis thaliana seedlings. The amount of fomannoxin in H. abietinum 331-AcH 505 dual cultures was reduced compared to axenic fungus cultures and fungus-plant dual cultures. Following addition of fomannoxin to AcH 505 cultures, the compound disappeared and three novel fomannoxin derivatives without phytotoxic activity were detected. Another novel compound, fomannoxin amide, was discovered following fomannoxin addition to GB 4-2 cultures. Nine other streptomycetes converted fomannoxin into fomannoxin acid or fomannoxin amide. Both compounds exhibit the same phytotoxicity as fomannoxin. We, thus, conclude that the streptomycete-mediated modulation of spruce infection with H. abietinum 331 does not depend on the availability of fomannoxin. We further add evidence to the observation that the lipophilic side chain of fomannoxin is an important structural element for its phytotoxicity.

Host responses in Norway spruce roots induced to the pathogen Ceratocystis polonica are evaded or suppressed by the ectomycorrhizal fungus Laccaria bicolor

The outcome of a compatible mycorrhizal interaction is different from that in a compatible plant-pathogen interaction; however, it is not clear what mechanisms are used to evade or suppress the host defence. The aim of this work is to reveal differences between the interaction of Norway spruce roots to the pathogen Ceratocystis polonica and the ectomycorrhizal Laccaria bicolor, examine if L. bicolor is able to evade inducing host defence responses typically induced by pathogens, and test if prior inoculation with the ectomycorrhizal fungus affects the outcome of a later challenge with the pathogen. The pathogen was able to invade the roots and caused extensive necrosis, leading to seedling death, with or without prior inoculation with L. bicolor. The ectomycorrhizal L. bicolor colonised primary roots of the Norway spruce seedlings by partly covering, displacing and convoluting the cells of the outer root cortex, leaving the seedlings healthy. We detected increased total peroxidase activity, and staining indicating increased lignification in roots as a response to C. polonica. In L. bicolor inoculated roots there was no increase in total peroxidase activity, but an additional highly acidic peroxidase isoform appeared that was not present in healthy roots, or in roots invaded by the pathogen. Increased protease activity was detected in roots colonised by C. polonica, but little protease activity was detected in L. bicolor inoculated roots. These results suggest that the pathogen efficiently invades the roots despite the induced host defence responses, while L. bicolor suppresses or evades inducing such host responses in this experimental system.

Wheat drought-responsive grain proteome analysis by linear and nonlinear 2-DE and MALDI-TOF mass spectrometry

A comparative proteomic analysis of drought-responsive proteins during grain development of two wheat varieties Kauz (strong resistance to drought stress) and Janz (sensitive to drought stress) was performed by using linear and nonlinear 2-DE and MALDI-TOF mass spectrometry technologies. Results revealed that the nonlinear 2-DE had much higher resolution than the linear 2-DE. A total of 153 differentially expressed protein spots were detected by both 2-DE maps, of which 122 protein spots were identified by MALDI-TOF and MALDI-TOF/TOF mass spectrometry. The identified differential proteins were mainly involved in carbohydrate metabolism (26%), detoxification and defense (23%), and storage proteins (17%). Some key proteins demonstrated significantly different expression patterns between the two varieties. In particular, catalase isozyme 1, WD40 repeat protein, LEA and alpha-amylase inhibitors displayed an upregulated expression pattern in Kauz, whereas they were downregulated or unchanged in Janz. Small and large subunit ADP glucose pyrophosphorylase, ascorbate peroxidase and G beta-like protein were all downregulated under drought stress in Janz, but had no expression changes in Kauz. Sucrose synthase and triticin precursor showed an upregulated expression pattern under water deficits in both varieties, but their upregulation levels were much higher in Kauz than in Janz. These differentially expressed proteins could be related to the biochemical pathways for stronger drought resistance of Kauz.

Abscisic acid enhances resistance to Alternaria solani in tomato seedlings

The plant hormone abscisic acid (ABA) is an important regulator in many aspects of plant growth and development, as well as stress resistance. Here, we investigated the effects of exogenous ABA application on the interaction between tomato (Solanum lycopersicon L.) and Alternaria solani (early blight). Foliar spraying of 7.58 μM ABA was effective in reducing disease severity in tomato plants. Previously, increased activities of phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO) and peroxidase (POD) were observed in exogenous ABA-treated tomato leaves. Moreover, these enzyme activities were maintained at higher levels in ABA-pretreated and A. solani challenged tomato plants. Tomato defense genes, such as PR1, β-1, 3-glucanase (GLU), PPO, POD, and superoxide dismutase (SOD), were rapidly and significantly up-regulated by exogenous ABA treatment. Furthermore, a subsequent challenge of ABA-pretreated plants with the pathogen A. solani resulted in higher expression of defense genes, compared to water-treated or A. solani inoculated plants. Therefore, our results suggest that exogenous ABA could enhance disease resistance against A. solani infection in tomato through the activation of defense genes and via the enhancement of defense-related enzymatic activities.

Identification, characterization, and expression analyses of class II and IV chitinase genes from Douglas-fir seedlings infected by Phellinus sulphurascens

Laminated root rot (LRR) disease, caused by the fungus Phellinus sulphurascens, is a major threat to coastal Douglas-fir (DF) (Pseudotsuga menziesii) forests in western North America. Understanding host-pathogen interactions of this pathosystem is essential to manage this important conifer root disease. Our research objectives were to identify DF pathogenesis-related (PR) genes and analyze their expression patterns over the course of infection. We constructed a cDNA library of Phellinus sulphurascens-infected DF seedling roots and sequenced a total of 3,600 random cDNA clones from this library. One of the largest groups of identified genes (203 cDNA clones) matched with chitinase genes reported in other plant species. We identified at least three class II and six class IV chitinase genes from DF seedlings. Quantitative reverse-transcriptase polymerase chain reaction analyses showed significant differential expression patterns locally in root tissues and systemically in needle tissues after fungal invasion. Nonetheless, there was a common trend in gene expression patterns for most of the chitinase genes: an upregulation within 12 h of pathogen inoculation followed by down-regulation within 2 to 3 days postinoculation (dpi), and then further upregulation within 5 to 7 dpi. Western immunoblot data showed differential accumulation of class IV chitinases in Phellinus sulphurascens-infected DF seedlings. Further detailed functional analyses will help us to understand the specific role of DF chitinases in defense against Phellinus sulphurascens infection.

Molecular cloning of peroxidase cDNAs from dehydration-treated fibrous roots of sweetpotato and their differential expression in response to stress

Three peroxidase (POD) cDNAs were isolated from dehydration-treated fibrous roots of sweetpotato (Ipomoea batatas) plant via the screening of a cDNA library, and their expressions were assessed to characterize functions of each POD in relation to environmental stress. Three PODs were divided into two groups, designated the basic PODs (swpb4, swpb5) and the anionic PODs (swpa7), on the basis of the pI values of mature proteins. Fluorescence microscope analysis indicated that three PODs are secreted into the extracellular space. RTPCR analysis revealed that POD genes have diverse expression patterns in a variety of plant tissues. Swpb4 was abundantly expressed in stem tissues, whereas the expression levels of swpb5 and swpa7 transcripts were high in fibrous and thick pigmented roots. Swpb4 and swpa7 showed abundant expression levels in suspension cultured cells. Three POD genes responded differently in the leaf and fibrous roots in response to a variety of stresses including dehydration, temperature stress, stress-associated chemicals, and pathogenic bacteria.

Root inoculation with a forest soil streptomycete leads to locally and systemically increased resistance against phytopathogens in Norway spruce

Soil streptomycetes are commonly antagonistic against plant pathogens. However, interactions involving increased defense responses in the host plant, leading to suppression of plant disease development, have not yet been detailed. Here, the mechanisms were studied of disease suppression by Streptomyces sp. GB 4-2 against Heterobasidion root and butt rot in Norway spruce (Picea abies) seedlings. GB 4-2 promoted mycelial growth of the phytopathogenic fungus, germination rate of fungal spores, extension of germ tubes and early colonization of outer cortical layers of the plant root. Reduced colonization of the inner cortical cell layers was accompanied by the induction of cell wall appositions, and increased xylem formation in the vascular cylinder emerged after bacterium-fungus coinoculation. Bacterial treatment led to decreased water content in roots and needles and increased photosynthetic yield (F(v)/F(m)) and peroxidase activities in needles. The infection of needles by Botrytis cinerea was reduced by bacterial pretreatment. Complex interactions of GB 4-2 with Norway spruce and Heterobasidion abietinum were discovered. The bacterium promoted the growth of the phytopathogenic fungus but induced plant defense responses. Host responses indicate that GB 4-2 induces both local and systemic defense responses in Norway spruce.

Peroxidase activity and inducibility in the sea fan coral exposed to a fungal pathogen

The enzymatic defense mechanisms of Gorgonia ventalina to the fungal pathogen Aspergillus sydowii may play important roles in colony resistance to infection. In this study, we examined the role of the superfamily of peroxidase enzymes in the coral response to a naturally occurring pathogen. We examined the inducibility of peroxidases by experimentally exposing corals to A. sydowii and found that peroxidase activity was induced after an 8 day incubation period. In contrast, naturally infected corals collected from the reef had lower peroxidase activity when compared to healthy corals. Infected sea fans from the field also had less measurable protein in their tissues and increased purple sclerites near infection sites and it is likely that these infections are months old. Using native-PAGE activity gels, we detected 5 peroxidase isozymes in healthy corals, indicating that multiple isoforms of peroxidase with a plurality of possible functions are present in this coral. The role of the peroxidase enzymes in disease resistance was examined by testing anti-fungal activity of commercially available and partially purified sea fan peroxidases. In both cases there was significant, dose-dependent anti-fungal activity. While peroxidases are ubiquitous enzymes involved in many cellular pathways, we also hypothesize that G. ventalina utilizes these enzymes as an integral component in disease resistance pathways. As such, they may also contribute to the initiation of physiochemical defenses such as melanization and lipid soluble anti-fungal metabolites.

Suppression of plant defence response by a mycorrhiza helper bacterium

The aim of the present study was to determine whether the mycorrhiza helper bacterium Streptomyces sp. AcH 505 could serve as a biocontrol agent against Heterobasidion root and butt rot. Bacterial influence on mycelial growth of Heterobasidion sp. isolates, on the colonization of wood discs and Norway spruce (Picea abies) roots was determined. The effect of AcH 505 on plant photosynthesis, peroxidase activity and gene expression, and needle infections were investigated. AcH 505 was antagonistic to 11 of 12 tested fungal Heterobasidion isolates. The antagonism resulted in a suppression of fungal colonization of Norway spruce roots and wood discs. Mycelial growth rate of the 12th strain, Heterobasidion abietinum 331 was not affected by AcH 505, and colonization of roots by this fungal strain was promoted by AcH 505. Bacterial inoculation led to decreased peroxidase activities and gene expression levels in roots. AcH 505 promotes plant root colonization by Heterobasidion strains that are tolerant to antifungal metabolites produced by the bacterium. This may result from unknown bacterial factors that suppress the plant defence response.

Conifer defence against insects: microarray gene expression profiling of Sitka spruce (Picea sitchensis) induced by mechanical wounding or feeding by spruce budworms (Choristoneura occidentalis) or white pine weevils (Pissodes strobi) reveals large-scale changes of the host transcriptome

Conifers are resistant to attack from a large number of potential herbivores or pathogens. Previous molecular and biochemical characterization of selected conifer defence systems support a model of multigenic, constitutive and induced defences that act on invading insects via physical, chemical, biochemical or ecological (multitrophic) mechanisms. However, the genomic foundation of the complex defence and resistance mechanisms of conifers is largely unknown. As part of a genomics strategy to characterize inducible defences and possible resistance mechanisms of conifers against insect herbivory, we developed a cDNA microarray building upon a new spruce (Picea spp.) expressed sequence tag resource. This first-generation spruce cDNA microarray contains 9720 cDNA elements representing c. 5500 unique genes. We used this array to monitor gene expression in Sitka spruce (Picea sitchensis) bark in response to herbivory by white pine weevils (Pissodes strobi, Curculionidae) or wounding, and in young shoot tips in response to western spruce budworm (Choristoneura occidentalis, Lepidopterae) feeding. Weevils are stem-boring insects that feed on phloem, while budworms are foliage feeding larvae that consume needles and young shoot tips. Both insect species and wounding treatment caused substantial changes of the host plant transcriptome detected in each case by differential gene expression of several thousand array elements at 1 or 2 d after the onset of treatment. Overall, there was considerable overlap among differentially expressed gene sets from these three stress treatments. Functional classification of the induced transcripts revealed genes with roles in general plant defence, octadecanoid and ethylene signalling, transport, secondary metabolism, and transcriptional regulation. Several genes involved in primary metabolic processes such as photosynthesis were down-regulated upon insect feeding or wounding, fitting with the concept of dynamic resource allocation in plant defence. Refined expression analysis using gene-specific primers and real-time PCR for selected transcripts was in agreement with microarray results for most genes tested. This study provides the first large-scale survey of insect-induced defence transcripts in a gymnosperm and provides a platform for functional investigation of plant-insect interactions in spruce. Induction of spruce genes of octadecanoid and ethylene signalling, terpenoid biosynthesis, and phenolic secondary metabolism are discussed in more detail.

Cytological and enzymatic responses to aluminium stress in root tips of Norway spruce seedlings

•  Aluminium (Al) stress reduces plant growth. However, some species such as Norway spruce (Picea abies) seem to tolerate high Al concentrations. The aim of this study was to investigate characteristics possibly involved in Al tolerance in Norway spruce seedlings. •  Seedlings (10-d-old) were exposed to Al³⁺ concentrations of 0.5 and 5 mm for up to 168 h. The effect of Al stress on root growth, cell morphology and Al distribution, callose production, and peroxidase and chitinase activity was analysed. •  Root growth decreased after 1 d and 2 d with 5 and 0.5 mm Al, respectively. Callose concentration increased strongly after 6 h treatment with 5 mm Al. The activity of many peroxidase and chitinase isoforms decreased after 1-24 h exposure of both treatments. Several isoforms increased after 48-168 h exposure to 5 mm Al. •  We postulate that, with external Al concentrations 0.5 mm or lower, an increased production above constitutive levels of peroxidase or chitinase is not required for Al tolerance in young Norway spruce seedlings. High constitutive levels of peroxidase and chitinase in this species may be part of this Al tolerance.